In advanced radio telecommunication networks, a resource scheduling adaptation with respect to a connected radio communication device or user equipment, UE, is performed based on feedback information received from the UE.
As an example, according to 3GPP, Technical Specification 36.213, version 12.3.0, in the following being referred to as TS 36.213, the UE shall perform a periodic and/or an aperiodic reporting of indicators comprising a channel quality indicator, CQI, and a rank indicator, RI, to inform the radio access network node about the UE's radio conditions. This information may be used by the radio access network for scheduling decisions (e.g. comprising a selection of a modulation and coding scheme, MCS, to be used by the UE for receiving or transmitting a certain transport block, and a resource block, RB, allocation to the UE) to ensure an efficient usage of radio resources.
According to present paradigms, the network will usually perform a scheduling to ensure a maximum data throughout given the current channel conditions and UE capabilities. Thereto, as e.g. defined in section 7.2.3 of TS 36.213, the UE shall report to the radio terminating node of radio access network, i.e. the eNB, the highest wideband CQI value within the range of suitable CQI values matching to the instantaneous radio conditions experienced by the UE given the receiver capabilities of the UE, resulting into a block error rate, BLER, equal or below 10%. The BLER therein may represent a ratio of a number of erroneous data blocks and a corresponding total number of received data blocks. The radio access network will use the reported CQI value as one input to its scheduling algorithm. As defined in above-cited TS 36.213, there are 15 CQI values from 0 to 15 each associated to a certain efficiency, wherein the efficiently increases with the value.
Reporting such “maximum” CQI value may result in high or aggressive MCS and RB allocation with high code rates by the eNodeB. In certain conditions however, such resource allocation may result in a high BLER beyond the defined maximum BLER, especially in situations of frequency selective fading channels, where the channel in frequency domain has large variance. As a consequence, a single downlink (DL) transport block (TB) might be sent with too high allocation and some or even all HARQ retransmissions might fail.
In case of a short duration signaling connection, the connection may be released before the signaling data from the UE may be successfully received by the network. Such behavior may have a high impact on the system performance.
As an example, according to 3GPP TS 24.301, version 12.6.0, several scenarios are defined, wherein a UE shall perform a tracking area update, TAU procedure. In some scenarios, e.g. in a scenario as shown in FIG. 1, a radio connection is established just to perform TAU procedure, e.g. when a UE 10 enters into a new tracking area if no user data is pending.
Thereto, the UE 10 may send an evolved packet system (EPS) Mobility Management (EMM) TAU REQUEST message S1 with old context (e.g. a Globally Unique Temporary ID, GUTI, according to LTE specifications, allocated by a previous mobility management entity (MME) to the UE 10) to a base station or eNodeB 11 that forwards this message to an (actual) MME. After performing an RRC connection setup communication S2 with the base station 11, and an EMM authentication communication S3, and an EMM security communication S4 with the MME, The MME sends a TRACKING AREA UPDATE COMPLETE message S5 with new context (over the eNodeB 11) to the UE 10. The UE 10 sends a TAU COMPLETE message S6 to the eNodeB 11, and the eNodeB 11 replies with a RLC status report S7 to acknowledge reception of TAU COMPLETE message and a RRC CONNECTION RELEASE message S8 to release the LTE connection.
The UE non-access stratum, NAS, layer within the UE 10 must know if the TAU COMPLETE message has been received correctly by the network. The UE 10 may derive this information from a reception of the RLC status report (RLC ACK) for the UL transmission of the TAU COMPLETE message. If, as consequence of too high allocation, the transport block containing this RLC status report cannot be received/decoded correctly by UE 10 as depicted in FIG. 1, the UE cannot judge if the previous transmission of the TAU COMPLETE message was successfully received by the network. With the reception of the RRC CONNECTION RELEASE message S8 there is also no possibility to request a new RLC status report. The UE will repeat the TAU procedure by re-sending a TAU Request with old context S9 which will however be rejected by the network that correspondingly sends a TAU REJECT message S11 and a further RRC CONNECTION RELEASE message S12 to the UE 10. As a consequence, a time and resource consuming a re-attach procedure is required.